Control method for roller quenching process of heavy-piece weight and large-section ultra-heavy plate

ABSTRACT

A control method for a roller quenching process of a heavy-piece weight and large-section ultra-heavy plate has a specific heat model, heat transfer coefficient model, temperature field model and correction model. Plate parameters inputted include thickness, length and carbon content, technological procedure, roller speed and acceleration. Measured parameters include tapping temperature, temperature after air cooling and temperature after self-tempering. The temperature field model is used. Specific heat model and the heat transfer coefficient model are invoked for calculating an air cooling stage, water cooling stage and self-tempering stage in sequence. Temperature fields are corrected through the correction model. Simulated results include a group of cooling curves and cooling speed curves at different thicknesses. Practical temperature drop curves and cooling speed curves are obtained in combination with actual production and part of actual debugging process is replaced by model calculation.

TECHNICAL FIELD

The present invention belongs to the technical field of metallurgy, andrelates to a control method for a roller quenching process of a plate.

BACKGROUND

The temperature field distribution after quenching of an ultra-heavyplate affects the physical performance and the machining performance ofthe plate to a large extent. In traditional immersion quenching, theplate is immersed into a quenching pool or quenching tank, which islimited by the volume of a container and causes low cooling speed anduneven distribution. In roller quenching, the plate enters a quenchingmachine through a rotating roller, and a high-pressure jet is sprayed onthe surface of the plate. Compared with the traditional quenching, theroller quenching substantially increases cooling speed and the plate canbe cooled to room temperature in short time. However, due to largethickness and slow heat transfer of the plate, there is a largetemperature difference between the center and the surface andperformance distribution is uneven after quenching. Calculation of thequenching process can better improve this problem. By setting differentparameters, the temperature curve and the cooling speed curve of theplate are calculated, and the temperature distribution and cooling speedchanges of the plate in different positions in the cooling process areintuitively observed. Calculated results can better serve the productionand reduce the production cost.

Patent CN105445319A discloses a method and a device for measuring awater cooling heat transfer coefficient of a plate surface. Imageinformation of a non-water-cooled surface of the plate is collected byan infrared thermal imager to obtain an actual cooling curve of thenon-water-cooled surface. The whole process from the water-cooledsurface to the non-water-cooled surface is simulated by finite element,and the water-cooled heat transfer coefficient is continuously adjustedto obtain a simulated cooling curve of the non-water-cooled surface.Patent CN102507636A discloses a method for measuring an interface heattransfer coefficient of steel in a rapid cooling process. A thermocoupleis connected to a temperature collection module through spot welding toobtain temperature change data of the surface. Heat treatment softwareis used to obtain the interface heat transfer coefficient in the coolingprocess and to simulate temperature change in the cooling process ofworkpieces. The simulated result is compared with a measured resultuntil a change tendency is fitted well. The prior art does not involveany control method related to a roller quenching process of aheavy-piece weight and large-section ultra-heavy plate, and any specificmethod to correct the heat transfer coefficient in the roller quenchingprocess of the heavy-piece weight and large-section ultra-heavy plate byusing a correction model.

SUMMARY

The purpose of the present invention is to provide a control method fora roller quenching process of a heavy-piece weight and large-sectionultra-heavy plate. The method is suitable for model control of theultra-heavy plate in a quenching process, is used for visuallyrepresenting the temperature change and cooling speed change of a headand a tail of the plate on the surface, the quarter thickness and thecenter of the plate through curves in combination with actual productionbased on a mathematical model, and can be used for guiding adjustment ofa technological procedure, saving production cost and obtaining aproduct with good plate shape.

The specific technical solution of the present invention is: a controlmethod for a roller quenching process of a heavy-piece weight andlarge-section ultra-heavy plate comprises the following steps:

step 1. reading plate information and process parameters, comprisingplate thickness, length, carbon content, roller speed and acceleration;

step 2. setting an initial heat transfer coefficient, using atemperature drop calculation model, invoking a specific heat model and aheat transfer coefficient model, correcting a heat transfer coefficientof an air cooling stage using a correction model of the heat transfercoefficient according to a measured temperature drop of the air coolingstage and then obtaining a temperature field of the air cooling stage;

step 3. determining a heat transfer coefficient of a water coolingstage, comprising determining a water cooling heat transfer coefficientof a high pressure section and determining a water cooling heat transfercoefficient of a low pressure section, wherein the water cooling heattransfer coefficient of the high pressure stage is determined; thequenching machine in the high pressure stage has the main action ofrapidly cooling the surface temperature of the plate to a lowertemperature; because the action time of the high pressure stage is muchlower than that of the low pressure stage and cannot be directlyobtained in actual production, empirical data is obtained fromexperiments;

the water cooling heat transfer coefficient of the low pressure stage isdetermined; when the plate leaves the quenching machine, only surfacetemperature is directly obtained; the plate surface has violenttemperature change at the beginning of quenching only in the quenchingprocess; after that, the temperature tends to be stable and is close tothe temperature of a convection medium until the plate leaves thequenching machine; thus, the convective heat transfer coefficient cannotbe directly calculated. The temperature inside the plate cannot bedirectly obtained. Thus, the water cooling heat transfer coefficientcannot be directly calculated through the water cooling stage. When theplate leaves the quenching machine, the inside temperature is stillhigher than the surface temperature and the inside temperature istransmitted to the plate surface by means of thermal conduction. Thus,the heat transfer coefficient of a water cooling stage of the lowpressure stage is corrected using the correction model of the heattransfer coefficient at self-tempering temperature of the surface duringair cooling after quenching. a specific method comprises: using atemperature field after tapping and air cooling as an initialtemperature field of the water cooling stage; giving an initial heattransfer coefficient of the low pressure section; calculating thetemperature field; using a temperature field after water cooling as aninitial temperature field of a self-tempering stage for calculating atemperature value of a self-tempered surface node; comparing thetemperature value with a measured value; invoking the correction modelof the heat transfer coefficient for correcting the water cooling heattransfer coefficient; keeping the air cooling heat transfer coefficientunchanged; reusing the temperature drop calculation model; and invokingthe specific heat model and the heat transfer coefficient model forcalculating the temperature field of the water cooling stage and thetemperature field of the self-tempering stage until a difference valueis within a permissible error; and

step 4. obtaining temperature drop curves and cooling speed curves ofdifferent positions in line with the actual situation in the platequenching process.

Because the convective heat transfer coefficient in the quenchingprocess cannot be directly measured, the calculated temperature and themeasured temperature need to be compared and the heat transfercoefficient is corrected using the correction model so as to correct thetemperature field. The correction model of the heat transfer coefficientin above step 2 and step 3 is as follows:

an interval range [0, A] of the initial heat transfer coefficient isgiven; an upper limit value A is taken as the initial heat transfercoefficient for calculating the temperature field; if a computed valueis higher than a target value, a range [A, 1.5A] of the heat transfercoefficient is taken; the upper limit value of a previous interval istaken as a lower limit value of a new interval in each interval change,and 1.5 times of the lower limit value of the new interval is taken asan upper limit value of the new interval until the value of the heattransfer coefficient is the upper limit of the interval and the computedvalue is lower than the target value; this indicates that the actualconvective heat transfer coefficient is within this interval at thismoment; in the interval, a golden section method is used to continuouslyreduce the interval until the difference value between the measuredvalue and the target value is within the permissible error; and at thismoment, the heat transfer coefficient value is an actual value.

Further, in above steps 2 and 3:

1) calculation of the specific heat model: the specific heat coefficientis mainly relevant to the carbon content and the temperature of theplate; a set definite value is taken as the definition scope of thecarbon content; when the carbon content is not the above value, left andright boundary values corresponding to the carbon content are determinedat first; the weight of the carbon content is determined byinterpolation; and then the interval of the temperature is compared,thereby determining a specific heat value of the plate;

2) calculation of the heat transfer coefficient model: firstly, specificheat values and heat transfer coefficient values of plates withdifferent carbon contents at different temperatures are obtained throughexperiments; and then specific heat values and heat transfer coefficientvalues corresponding to other carbon contents and other temperatures aredetermined by interpolation;

3) the temperature drop calculation model is as follows:

a one-dimensional unsteady heat transfer differential equation in acartesian coordinate system is established:

$\begin{matrix}{\frac{\partial T}{\partial t} = {{a\frac{\partial^{2}T}{\partial x^{2}}} + {\overset{.}{Q}\mspace{14mu} \left( {{0 < x < d},{t > 0}} \right)}}} & \; \\{wherein} & \; \\{a = \frac{\lambda}{\rho \; c}} & \;\end{matrix}$

x is the length of a divided cell; d is the thickness of the plate; t isthe time; T is the temperature; a is a temperature conductivity; {dotover (Q)} is an internal heat source; λ is a heat transfer coefficientof a quenching plate; ρ is the density of the quenching plate; c is thespecific heat of the quenching plate;

during calculation, latent heat of phase change in the cooling processof the plate is counted into the mean specific heat; therefore, theinternal heat source can be neglected;

an initial condition is:

T(x,0)=T0 (0<x<d, t>0)

boundary conditions are:

$\quad\left\{ \begin{matrix}{\left. {{- \lambda}\frac{\partial{T\left( {x,t} \right)}}{\partial x}} \right|_{x = 0} = {h_{x}\left( {{T\left( {0,t} \right)} - T_{f}} \right)}} & \left( {{x = 0},{t > 0}} \right) \\{\left. {{- \lambda}\frac{\partial{T\left( {x,t} \right)}}{\partial x}} \right|_{x = d} = {h_{x}\left( {{T\left( {d,t} \right)} - T_{f}} \right)}} & \left( {{x = d},{t > 0}} \right)\end{matrix} \right.$

in order to improve the convergence and stability of Fourier number andmake the model have a smaller error, Crank-Nicolson difference method isused;

${{\frac{1}{2}\left( \frac{\partial^{2}T}{\partial x^{2}} \right)_{i}^{t}} + {\frac{1}{2}\left( \frac{\partial^{2}T}{\partial x^{2}} \right)_{i}^{t + 1}}} = {\frac{1}{a}\left( \frac{\partial T}{\partial\tau} \right)_{i}^{t}}$

t is the time; i is a node, 0≤i≤I; the temperature field is establishedas follows:

an internal node is:

−F _(ox) T _(i+1) ^(t+1)(2+2F _(ox))T _(i) ^(t+1) −F _(ox) T _(i−1)^(t+1) =F _(ox) T _(i+1) ^(t)+(2−2F _(ox))T _(i) ^(t) +F _(ox) T _(i−1)^(t)

a boundary node is:

$\begin{matrix}{{{{- F_{ox}}T_{i - 1}^{t + 1}} + {\left( {1 + F_{ox} + {F_{ox}B_{ix}}} \right)T_{i}^{t + 1}}} = {{F_{ox}T_{i - 1}^{t}} + {\left( {1 - F_{ox} - {F_{ox}B_{ix}}} \right)T_{i}^{t}} + {2F_{ox}B_{ix}T_{f}}}} & \; \\{wherein} & \; \\\begin{matrix}{F_{ox} = \frac{{a\; \Delta \; t}\;}{\Delta \; x^{2}}} & {B_{ix} = \frac{h_{x}\Delta \; x}{\lambda}}\end{matrix} & \;\end{matrix}$

h_(x) is a convective heat transfer coefficient; T_(f) is a watertemperature; T_(i) ^(t) is a temperature value corresponding to the ithnode of the plate at time oft; F_(ox) is the Fourier number; B_(ix) is aBiot number;

stability conditions are:

$\quad\left\{ \begin{matrix}{{1 - F_{ox}} \geqq 0} \\{{1 - F_{ox} - {F_{ox}B_{ix}}} \geqq 0}\end{matrix} \right.$

when the initial temperature field and the heat transfer coefficient areknown, the temperature distribution at any node and at any moment iscalculated by difference.

Further, cooling time in the above temperature drop calculation model iscontrolled as follows: the model of the plate conducts calculationaccording to the roller position of the plate in three parts: an aircooling stage before entering a quenching machine, a quenching stagewhen entering the quenching machine and a self-tempering stage afterentering the quenching machine;

the time of the air cooling stage is determined as follows: the platehas certain length; different positions take different times to enterthe quenching machine. Thus, a head and a tail are respectivelycalculated; the head of the plate moves at uniform speed before enteringthe quenching machine, and thus calculation is conducted through adistance from the head to the quenching machine and initial speed; afterthe head of the plate enters the quenching machine, a roller begins toapply a certain acceleration; thus, the tail of the plate begins toaccelerate in the air cooling stage; at this moment, the distance fromthe quenching machine is the length of the plate; the air cooling timefor the tail is calculated through the initial seed, the distance andthe acceleration;

the time of the quenching stage is determined as follows: the time ofthe quenching stage is divided into a time to go through the highpressure stage and a time to go through the low pressure stage; firstly,the length of the high pressure stage is determined; the quenching timeof the head of the plate is directly calculated according to the setinitial speed and acceleration of the roller; because the plate isaccelerated immediately when the head of the plate enters the quenchingmachine, the speed at which the tail enters the quenching machine isdetermined through the time and the acceleration of the air coolingacceleration part; the time to go through the high pressure stage iscalculated according to the speed and the acceleration; the timerequired for the plate to go through the low pressure stage isdetermined according to swing time; and

the time of the self-tempering stage is determined as follows: aspecific method comprises: timing with a chronograph when the plateleaves the quenching machine; measuring the self-tempering temperaturein the same position of the plate at different moments; stopping timingafter self-tempering; taking a maximum self-tempering temperature as atarget temperature in analog calculation; and taking a correspondingtime as the time of the self-tempering stage.

Further, an initial temperature field model of each stage in steps 2 and3 is established as follows: the temperature when the plate leaves afurnace is taken as an initial temperature field of the air coolingstage; a simulated temperature field after air cooling calculated by thetemperature field model is compared with the temperature measured at atemperature measurement point before entering the quenching machine andcorrected; finally, a practical temperature field after air cooling isobtained and is taken as an initial temperature field of the watercooling stage; the water cooling stage requires no correctioncomputation; and a model calculation result is directly transmitted tothe self-tempering stage as the initial temperature field of theself-tempering stage.

Further, the output result in step 4 comprises heat transfer coefficientvalues of the air cooling stage, the water cooling high pressure stageand the water cooling low pressure stage, temperature change curves andcooling speed change curves of surfaces, quarters and centers of thehead and the tail of the plate.

The present invention has the following advantages:

1) Initial parameters conform to the actual production procedure.

Considering site production conditions, required measured data can bedirectly obtained in production.

2) The calculated results of each stage are corrected according to themeasured values, and the calculated results are closer to the actualcooling curve of the plate.

3) The output result comprises the cooling curves and the cooling speedcurves at different thicknesses, which can more visually show thetemperature difference of the center and the surface, the cooling speeddifference of the center and the surface, the temperature differencebetween the head and the tail and the cooling speed difference betweenthe head and the tail, and can be used to guide and adjust theproduction process.

4) Part of site debugging is replaced by calculation to reduce energyconsumption and production cost.

DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of a calculation process.

FIG. 2 shows temperature change curves obtained by calculation.

FIG. 3 shows cooling speed change curves obtained by calculation.

FIG. 4 shows cooling speed change curves after the high pressure stageis filtered.

DETAILED DESCRIPTION

1) Input of parameters. Including plate parameters: thickness, lengthand carbon content; technological procedure: roller speed, acceleration,length of the high pressure stage of the quenching machine, tappingtemperature and initial value of a heat transfer coefficient; measuredparameters: tapping temperature, temperature before entering thequenching machine, self-tempering time and temperature afterself-tempering.

2) Determination of the air cooling stage, the quenching stage and theself-tempering stage. The plate has certain length; different positionstake different times to enter the quenching machine. Thus, a head and atail are respectively calculated; and the head of the plate moves atuniform speed before entering the quenching machine, accelerates afterentering the high pressure stage of the quenching machine and thenswings in the low pressure stage. The tail of the plate moves asfollows: the air cooling stage firstly moves at uniform speed beforeentering the quenching machine, and accelerates after the head of theplate enters the quenching machine; the high pressure stage accelerates,and then the low pressure stage swings. The time of the air coolingstage and the time of the high pressure stage are calculated through thedistance, the initial speed and the acceleration. The time of the lowpressure stage is determined through the set swing time. The time of theself-tempering stage is determined by means of timing.

3) Calculation of the temperature field of the air cooling stage. Theinitial temperature field is established by tapping temperature. Thespecific heat and the heat transfer coefficients of different nodes arerespectively calculated in each time step. Then, a temperature fieldmodel is invoked to calculate the air cooling temperature field. Thecalculated result is compared with the measured value. The correctionmodel is invoked to correct the air cooling heat transfer coefficient toobtain the temperature field after air cooling.

4) Determination of the time of the water cooling stage. Times requiredfor the head, the middle and the tail of the plate to go through thehigh pressure stage of the quenching machine are respectivelycalculated. The time required for the plate to go through the lowpressure stage is determined according to the swing time.

5) Calculation of the water cooling temperature field. The temperaturefield after water cooling is calculated by invoking the specific heatmodel, the heat transfer coefficient model and the temperature fieldmodel and using the calculated temperature field after air cooling asthe initial temperature field.

6) Calculation of the temperature field after self-tempering. Thespecific heat model, the heat transfer coefficient model and thetemperature field model are invoked to calculate the self-temperingtemperature field by using the temperature field after water cooling asthe initial temperature field and using the corrected air cooling heattransfer coefficient value as the heat transfer coefficient value. Thecalculated result is compared with the measured value. If the calculatedresult is not within a permissible error, the correction model isinvoked to correct the air cooling heat transfer coefficient forrecalculation of steps 5 and 6.

7) Output of the calculated result. The temperature drop curves and thecooling speed curves of the head surface and the tail surface, thequarter thickness and the center of the plate in the air cooling stageand the quenching stage are drawn.

Embodiment

The thickness of the plate is 132 mm; the length is 7250 mm; the carboncontent is 0.15%; the roller speed is 0.2 m/s; the acceleration is0.00015 m/s²; the length of the high pressure stage of the quenchingmachine is 3.2 m; the initial values of the heat transfer coefficientare: 100 W/(m²K) for the air cooling stage, 20000 W/(m²K) for the highpressure stage and 8000 W/(m²K) for the low pressure stage; watertemperature is 22.1° C.; tapping temperature is 910° C.; the temperaturebefore entering the quenching machine is 830° C.; air cooling time is 45s; the swing time of the low pressure stage is 1560 s; theself-tempering time is 142 s; and the temperature after self-temperingis 28° C. The length of a cell is 1 mm and the time step is 0.5 s. Thecalculation flow is shown in FIG. 1.

Calculated results: the heat transfer coefficient value of the aircooling stage is 124.64 W/(m²K) and the water cooling heat transfercoefficient value of the low pressure stage is 2250 W/(m²K). Thetemperature drop curves are shown in FIG. 2. It is known from the figurethat the surface temperature of the plate is rapidly reduced when theplate enters the air cooling stage and then enters the water coolinghigh pressure stage. After entering the low pressure stage, because theinside temperature is transmitted outwards, the temperature rises alittle. Compared with the surface, the temperature of the quarterthickness and the center is reduced slowly. The cooling speed curves areshown in FIG. 3. After the cooling speed curves are compared with thetemperature drop curves, it is found that in the high pressure stage,the cooling speed of the surface is rapidly increased; after enteringthe low pressure stage, the cooling speed curve has a negative value,which indicates that the temperature rises; short-time cooling speed ofthe surface is much higher than that of other moments, which is notconvenient for observing the cooling speed of other moments; thus, thecooling speed is shown in FIG. 4 after part of the cooling speed isfiltered; it is found that the cooling speed of the quarter thicknessand the center is gradually increased when the temperature differencebetween the center and the surface is larger; and after this, with thedecrease of the temperature, the cooling speed is gradually decreased.

1. A control method for a roller quenching process of a heavy-piece weight and large-section ultra-heavy plate, comprising the following steps: step
 1. reading plate information and process parameters, comprising plate thickness, length, carbon content, roller speed and acceleration; step
 2. setting an initial heat transfer coefficient, using a temperature drop calculation model, invoking a specific heat model and a heat transfer coefficient model, correcting a heat transfer coefficient of an air cooling stage using a correction model of the heat transfer coefficient according to a measured temperature drop of the air cooling stage and then obtaining a temperature field of the air cooling stage; step
 3. determining a heat transfer coefficient of a water cooling stage, comprising determining a water cooling heat transfer coefficient of a high pressure stage and determining a water cooling heat transfer coefficient of a low pressure stage, wherein the water cooling heat transfer coefficient of the high pressure stage is determined by empirical data from experiments; the water cooling heat transfer coefficient of the low pressure stage is determined by correcting the heat transfer coefficient of a water cooling stage of the low pressure stage using the correction model of the heat transfer coefficient at self-tempering temperature of the surface during air cooling after quenching; a specific method comprises: using a temperature field after tapping and air cooling as an initial temperature field of the water cooling stage; giving an initial heat transfer coefficient of the low pressure stage; calculating the temperature field; using a temperature field after water cooling as an initial temperature field of a self-tempering stage for calculating a temperature value of a self-tempered surface node; comparing the temperature value with a measured value; invoking the correction model of the heat transfer coefficient for correcting the water cooling heat transfer coefficient; keeping the air cooling heat transfer coefficient unchanged; reusing the temperature drop calculation model; and invoking the specific heat model and the heat transfer coefficient model for calculating the temperature field of the water cooling stage and the temperature field of the self-tempering stage until a difference value is within a permissible error; step
 4. obtaining temperature drop curves and cooling speed curves of different positions in line with the actual situation in the plate quenching process; the correction model of the heat transfer coefficient in above step 2 and step 3 is as follows: an interval range [0, A] of the initial heat transfer coefficient is given; an upper limit value A is taken as the initial heat transfer coefficient for calculating the temperature field; if a computed value is higher than a target value, a range [A, 1.5A] of the heat transfer coefficient is taken; the upper limit value of a previous interval is taken as a lower limit value of a new interval in each interval change, and 1.5 times of the lower limit value of the new interval is taken as an upper limit value of the new interval until the value of the heat transfer coefficient is the upper limit of the interval and the computed value is lower than the target value; this indicates that the actual convective heat transfer coefficient is within this interval at this moment; in the interval, a golden section method is used to continuously reduce the interval until the difference value between the measured value and the target value is within the permissible error; and at this moment, the heat transfer coefficient value is an actual value.
 2. The control method for the roller quenching process of the heavy-piece weight and large-section ultra-heavy plate according to claim 1, wherein cooling time in the temperature drop calculation model is controlled as follows: the model of the plate conducts calculation according to the roller position of the plate in three parts: an air cooling stage before entering a quenching machine, a quenching stage when entering the quenching machine and a self-tempering stage after entering the quenching machine; the time of the air cooling stage is determined as follows: a head and a tail are respectively calculated; the head of the plate moves at uniform speed before entering the quenching machine, and thus calculation is conducted through a distance from the head to the quenching machine and initial speed; after the head of the plate enters the quenching machine, a roller begins to apply a certain acceleration; thus, the tail of the plate begins to accelerate in the air cooling stage; at this moment, the distance from the quenching machine is the length of the plate; the air cooling time for the tail is calculated through the initial seed, the distance and the acceleration; the time of the quenching stage is determined as follows: the time of the quenching stage is divided into a time to go through the high pressure stage and a time to go through the low pressure stage; firstly, the length of the high pressure stage is determined; the quenching time of the head of the plate is directly calculated according to the set initial speed and acceleration of the roller; because the plate is accelerated immediately when the head of the plate enters the quenching machine, the speed at which the tail enters the quenching machine is determined through the time and the acceleration of the air cooling acceleration part; the time to go through the high pressure stage is calculated according to the speed and the acceleration; the time required for the plate to go through the low pressure stage is determined according to swing time; and the time of the self-tempering stage is determined as follows: a specific method comprises: timing with a chronograph when the plate leaves the quenching machine; measuring the self-tempering temperature in the same position of the plate at different moments; stopping timing after self-tempering; taking a maximum self-tempering temperature as a target temperature in analog calculation; and taking a corresponding time as the time of the self-tempering stage.
 3. The control method for the roller quenching process of the heavy-piece weight and large-section ultra-heavy plate according to claim 1, wherein an initial temperature field model of each stage in steps 2 and 3 is established as follows: the temperature when the plate leaves a furnace is taken as an initial temperature field of the air cooling stage; a simulated temperature field after air cooling calculated by the temperature field model is compared with the temperature measured at a temperature measurement point before entering the quenching machine and corrected; finally, a practical temperature field after air cooling is obtained and is taken as an initial temperature field of the water cooling stage; the water cooling stage requires no correction computation; and a model calculation result is directly transmitted to the self-tempering stage as the initial temperature field of the self-tempering stage.
 4. The control method for the roller quenching process of the heavy-piece weight and large-section ultra-heavy plate according to claim 1, wherein the output result in step 4 comprises heat transfer coefficient values of the air cooling stage, the water cooling high pressure stage and the water cooling low pressure stage, temperature change curves and cooling speed change curves of surfaces, quarters and centers of the head and the tail of the plate.
 5. The control method for the roller quenching process of the heavy-piece weight and large-section ultra-heavy plate according to claim 3, wherein the output result in step 4 comprises heat transfer coefficient values of the air cooling stage, the water cooling high pressure stage and the water cooling low pressure stage, temperature change curves and cooling speed change curves of surfaces, quarters and centers of the head and the tail of the plate.
 6. The control method for the roller quenching process of the heavy-piece weight and large-section ultra-heavy plate according to claim 1, wherein in the steps 2 and 3: 1) calculation of the specific heat model: the specific heat coefficient is mainly relevant to the carbon content and the temperature of the plate; a set definite value is taken as the definition scope of the carbon content; when the carbon content is not the above value, left and right boundary values corresponding to the carbon content are determined at first; the weight of the carbon content is determined by interpolation; and then the interval of the temperature is compared, thereby determining a specific heat value of the plate; 2) calculation of the heat transfer coefficient model: firstly, specific heat values and heat transfer coefficient values of plates with different carbon contents at different temperatures are obtained through experiments; and then specific heat values and heat transfer coefficient values corresponding to other carbon contents and other temperatures are determined by interpolation; 3) the temperature drop calculation model is as follows: a one-dimensional unsteady heat transfer differential equation in a cartesian coordinate system is established: $\begin{matrix} {\frac{\partial T}{\partial t} = {{a\frac{\partial^{2}T}{\partial x^{2}}} + {\overset{.}{Q}\mspace{14mu} \left( {{0 < x < d},{t > 0}} \right)}}} & \; \\ {wherein} & \; \\ {a = \frac{\lambda}{\rho \; c}} & \; \end{matrix}$ x is the length of a divided cell; d is the thickness of the plate; t is the time; T is the temperature; a is a temperature conductivity; {dot over (Q)} is an internal heat source; λ is a heat transfer coefficient of a quenching plate; ρ is the density of the quenching plate; C is the specific heat of the quenching plate; during calculation, latent heat of phase change in the cooling process of the plate is counted into the mean specific heat; therefore, the internal heat source can be neglected; an initial condition is: T(x,0)=T0 (0<x<d, t>0) boundary conditions are: $\quad\left\{ \begin{matrix} {\left. {{- \lambda}\frac{\partial{T\left( {x,t} \right)}}{\partial x}} \right|_{x = 0} = {h_{x}\left( {{T\left( {0,t} \right)} - T_{f}} \right)}} & \left( {{x = 0},{t > 0}} \right) \\ {\left. {{- \lambda}\frac{\partial{T\left( {x,t} \right)}}{\partial x}} \right|_{x = d} = {h_{x}\left( {{T\left( {d,t} \right)} - T_{f}} \right)}} & \left( {{x = d},{t > 0}} \right) \end{matrix} \right.$ in order to improve the convergence and stability of Fourier number and make the model have a smaller error, Crank-Nicolson difference method is used; ${{\frac{1}{2}\left( \frac{\partial^{2}T}{\partial x^{2}} \right)_{i}^{t}} + {\frac{1}{2}\left( \frac{\partial^{2}T}{\partial x^{2}} \right)_{i}^{t + 1}}} = {\frac{1}{a}\left( \frac{\partial T}{\partial\tau} \right)_{i}^{t}}$ t is the time; i is a node, 0≤i≤I; the temperature field is established as follows: an internal node is: −F _(ox) T _(i+1) ^(t+1)(2+2F _(ox))T _(i) ^(t+1) −F _(ox) T _(i−1) ^(t+1) =F _(ox) T _(i+1) ^(t)+(2−2F _(ox))T _(i) ^(t) +F _(ox) T _(i−1) ^(t) a boundary node is: $\begin{matrix} {{{{- F_{ox}}T_{i - 1}^{t + 1}} + {\left( {1 + F_{ox} + {F_{ox}B_{ix}}} \right)T_{i}^{t + 1}}} = {{F_{ox}T_{i - 1}^{t}} + {\left( {1 - F_{ox} - {F_{ox}B_{ix}}} \right)T_{i}^{t}} + {2F_{ox}B_{ix}T_{f}}}} & \; \\ {wherein} & \; \\ \begin{matrix} {F_{ox} = \frac{{a\; \Delta \; t}\;}{\Delta \; x^{2}}} & {B_{ix} = \frac{h_{x}\Delta \; x}{\lambda}} \end{matrix} & \; \end{matrix}$ h_(x) is a convective heat transfer coefficient; T_(f) is a water temperature; T_(i) ^(t) is a temperature value corresponding to the ith node of the plate at time of t; F_(ox) is the Fourier number; B_(ix) is a Biot number; stability conditions are: $\quad\left\{ \begin{matrix} {{1 - F_{ox}} \geqq 0} \\ {{1 - F_{ox} - {F_{ox}B_{ix}}} \geqq 0} \end{matrix} \right.$ when the initial temperature field and the heat transfer coefficient are known, the temperature distribution at any node and at any moment is calculated by difference. 